The present invention relates to a thermal head supporting means in a thermal recording apparatus, and, more particularly, relates to a supporting means of this type provided with a supporting mechanism and a head pressing mechanism, the supporting mechanism having a plurality of thermal heads aligned on one line and each having a linear array of thermal elements.
Heretofore, various types of thermal recording apparatus using at least one thermal head have been put into practice. Particularly, in one type having a plurality of thermal heads which is the subject of the present invention, the thermal heads are arranged side by side in the direction transverse the advancing direction of recording paper, so that multi-channel recording can be realized without reduction of recording width for example even in recording various kinds of analog waveforms.
Generally, a recording apparatus of the type using a plurality of thermal heads requires uniform contacting property between each thermal head and recording paper during the recording operation and moderate space-retaining property between each thermal head and a holder member for holding recording paper. In the prior art apparatus, various proposals have been made for satisfying such requirement.
For example, an apparatus is disclosed in Japanese Patent Unexamined Publication No. 55-97976 (1980). The apparatus is provided with a plurality of thermal heads arranged in the direction perpendicular to the paper feeding direction. The thermal heads are mounted on a crankshaft having a crank so that the thermal heads are collectively moved up and down when the crankshaft is driven by an electric motor.
In another embodiment of the above-mentioned apparatus, a slight play or gap is provided in a junction between each of the thermal heads and the crankshaft, and pressure is exerted on the thermal head by use of compression spings.
Further, a variety of apparatus similar to that mentioned above are disclosed in U.S. Pat. Nos. 4,145,698; 4,660,052; 4,205,395, etc.
In any case of the aforementioned conventional techniques, head supporting mechanisms are attached to the respective thermal heads in one-to-one correspondency. There arises therefore a problem in that it is difficult to make the contacting property between the respective thermal heads and recording paper uniform.
If uniform contacting property between the respective thermal head and recording paper is to be attained in the aforementioned prior art apparatus, it has been necessary to keep the associated constituent parts with high accuracy.
Further, the aforementioned prior art apparatus has another problem in that the freedom (or movable region) of each thermal head at its supporting portion is limited excessively.
For example, in the above Japanese Patent Unexamined Publication, there is only a description that a slight clearance is formed in the junction between each thermal head and the crankshaft in the apparatus disclosed therein.
In the apparatus disclosed in the above U.S. Pat. No. 4,145,698, since torsion-coiled springs are used to support the respective thermal heads, each thermal head has freedom only in the circumferential direction.